This invention relates to a system and method for recovering hydrocarbon fuel from hydrocarbon fuel bearing ores; particularly gasification recovery of oil from oil-bearing shale particularly recovery of oil from oil-bearing shale and coal gasification.
As the energy situation becomes more and more critical, it is important not only to conserve energy, but also to find every possible means of recovering energy from all sources available as economically and as efficiently as possible. In this regard, it is well-known that oil shales exist in large deposits which can be readily mined and pyrolyzed to produce shale oil and that there are large coal reserves; especially in the United States.
The term "oil shale" refers to marlstone, a limestone-like carbonaceous rock that can produce oil when heated to pyrolysis temperatures of about 800.degree. F.-1,000.degree. F. The oil precursor in the shale is an organic polymer substance of high molecular weight referred to as "kerogen". Oil shale is found all over the world and in at least 30 states in the United States with estimates of the amount of oil locked in those formations running into the trillions of barrels. In addition, a large amount of the oil shale formations in the United States with 25 to 30 or more gallons of oil per ton of shale can only be recovered by underground mining techniques.
Present techniques for producing oil from shale require large capital investment, pollution control, handling of raw and spent shale, and the need in some cases for large amounts of water to cool the hot kerogen vapors from the retort or kiln and to slurry and compact the spent shale back into the deposit.
In a modification of retorting applicable to underground mining referred to as in situ mining, a small portion of the rock is removed and the rest is reduced to small particles by explosives and then the particles are burned in place. The oil is collected at the bottom of the natural retort and pumped to the surface.
Regardless of the specific technique employed, in order to produce shale oil in large quantities, enormous expenditures are required with present state of the art techniques. One company estimates that it will have spent more than $100,000,000 by the time its first 9,500 barrel a day retort begins operating. Another company indicates that to produce 48,000 barrels of oil a day, it would need a half dozen 6 story tall retorts, each capable of processing 11,000 tons of shale a day. The company officials estimate that it will cost $1.3 billion to $1.5 billion for that operation. Still another company states that it has spent over $100,000,000 developing modified in situ technology for use at the shale sites and have been testing underground retorting for a number of years. The last three retorts built by this company were big enough for commercial product and were 160 feet square and almost 300 feet high. One collapsed. This company states that to scale operations up to commercial production, it would require 40 underground in situ retorts to produce the 50,000 barrels a day which was set as a goal.
There are at least six significant contributory factors to the continuing lack of economic feasibility for recovery of shale oil. These are high fixed costs of on-site construction of the necessary recovery plants (retorts and the like), the high carrying cost of the land necessary to support the large recovery plants, the uncertainties as to the technological feasibility of large plants due to problems arising from scaling up from small, successful pilot plants, the logistics of handling vast quantities of materials, the high risk premium on the cost of capital to carry out the recovery, and the environmental problems. These same factors have inhibited and largely prevented commercially-successful coal gasification.
Thus, it can be understood why no one in the last century has produced shale oil in the United States in other than small quantities, even though efforts to effect commercial production have been going on since the 1920's and particularly since the early 1970's.
As previously noted, the greatest available source of richest deposits of shale in the United States requires underground mining where it is expected that the usual mining techniques such as large room and pillar mining techniques will have to be used. This necessitates the dual problem of working to recover the shale and, further recovering the oil from the shale.
Another major problem with regard to extracting kerogen from shale is the problem of disposing of the spent shale. Having been exposed to the high temperatures in order to extract the oil, the shale expands in volume by a factor of as much as 150% and the original area mined cannot accomodate all of the expanded spent shale. Attempts to handle the shale by leaving them in dumps has not proven satisfactory. Aside from the unsightliness of such dumps, there is the problem of pollution due to the fact that rains on such dumps can produce a highly alkaline run-off. This necessitates the development of containment devices to prevent any such run-off. There is also the problem of landscaping and revegetation.
The same problems of massive capital expenditure also applies to efforts to make coal gasification a viable commercial reality in the United States even though the underlying technology exists.